Patent GB-181116-A (GB)
Abstract: 181,116. Relay Automatic Telephone Co., Ltd., Bryant, G. H., and Johnson, B. B. March 7, 1921. Automatic exchange systems.-In apparatus for connecting a calling line through an intermediate or link circuit to an idle one of another group of lines, if all the lines in the group are engaged when the call is initiated the calling line is prevented from obtaining connection to a line which becomes idle after the initiation of the call. Means are also provided for recording the number of times no line was available when a call was initiated, and for giving a signal to the calling party to indicate that all the trunks being busy he must replace his receiver. The invention is described as applied to a relay arrangement for connecting a calling subscriber's line S, Fig. 1, over an idle link L, Fig. 2, to an idle one of a group of outgoing trunks OT, Fig. 3. On a line, say S<5>, becoming a calling line, the line relay LE<5>, Fig. 1, is energized over circuit 1 to prepare circuit 2 and complete a circuit 3 for a test relay OTT<1>, Fig. 4, associated with the three outgoing trunks OT<1>, OT<2>, OT<3>, Fig. 3. A circuit 4 is thereby completed for the connecting relay OTC' of the first idle trunk also associated with an idle link L<1>. The link marking relay LM<1> responds in this circuit and completes the already prepared circuit 2 for the link connecting relay LC<1>. The relays LO<5> and OTC<1> extend the calling line S<5> to the trunk OT', and a loop across the calling line causes a relay (not shown) to operate, which transfers negative potential from the test wire T to the holding wire H, Fig. 3. A holding circuit 5, in which the link busy relay LB' and the cut-off relay CO' energize, is thereby completed for the connecting relays LC<5>, OTC<1>, circuits 1 2, 3, and 4 are broken, and the relays LE<5>, OTT<1>, and LM<1> de-energize. If the trunks OT', OT<2>, OT<3> are all either busy or associated with busy links when a subscriber calls, a connecting relay OTC<1>, OTC<2>, OTC<3> will not energize since either the test wire T will be devoid of negative potential, or the circuit 4 will be broken by a link busy relay LB. A link-marking relay LM will therefore not energize subsequent to the response of the test relay OTT', and a circuit 8 will be completed for a test relay OTT<2>, associated with the trunks OT<4>, OT<5>, OT<6>, which will be tested in the same manner as the trunks OT<1>, OT<2>, OT<3>, the relay OTT<2> holding in a circuit C<a> and de-energizing the test relay OTT<1>. If a trunk is available the call proceeds as before, but if all the trunks are either busy or associated with busy links, a link-marking relay LM will still not energize and a further circuit 11 will be completed for a relay ATB, Fig. 4, which locks up over circuit 11<a> and de-energizes the relay OTT<2>, The relay ATB, which is made slow-acting in order not to respond to impulses, causes a tone signal to be given to the calling party over circuits 13, 13<a>, operates a rscording device, and by breaking the energizing circuit of the test relay OTT' prevents the calling party SS or any line subsequently calling from having access to an outgoing trunk should one fall free, until the subscriber S<5> hangs up and disconnects the relays LE<5> and ATB. If the subscriber S<5> delays hanging up, the response of the relay MA lights a lamp in front of an attendant, who may release the connection by pressing to the right the armature Z of the relay F<5>, Fig. 1. A modification is described in which the omission of a subscriber to replace his receiver after receiving the tone signal does not prevent a subsequent caller from obtaining access to a trunk which falls free, as in the first arrangement. For this modification Fig. 5 should be substituted for Fig. 4. The contacts Z of the relays F of the calling lines are led to corresponding pairs of contacts Y of the relav ATB. which, if all trunks are unavailable, energizes as before in a circuit 11 but in series with a busy relay BB, which locks up and applies busy tone to the calling line. If the calling subscriber S<5> fails to hang up, the relay F<5> is energized over contacts Z, Y, and, breaking the circuit 8, de-energizes the relays OTT<2> and ATB, thus only keeping his own line out of service by disconnection of the circuit 3 by the relay F<5>. Specifications 181,117, 181,120, and 200,217 are referred to.